Converting oxygenates into light olefins is referred to as the oxygenate-to-olefin process. Non-limiting examples of oxygenates include methanol, ethanol, n-propanol, isopropanol, methyl ethyl ether, dimethyl ether, diethyl ether, di-isopropyl ether, formaldehyde, dimethyl carbonate, dimethyl ketone, acetic acid, and mixtures thereof. Non-limiting examples of olefins may be or include ethylene, propylene, and the like. Olefins are important petrochemicals used to make plastics or other chemicals, such as vinyl chloride, ethylene oxide, ethylbenzene, alcohols (with more carbon atoms than methanol and ethanol), acrylonitrile, propylene oxide, and the like.
There are numerous technologies available for producing oxygenate(s), including fermentation or reaction of synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal waste, or any other organic material. To produce methanol, a combustion reaction of natural gas, mostly methane, and an oxygen source having hydrogen, carbon monoxide and/or carbon dioxide produces synthesis gas. Synthesis gas production processes are well known, and include conventional steam reforming, autothermal reforming or a combination thereof. The synthesis gas may then be converted into methanol, for use in the oxygenate-to-olefin process.
The oxygenate-to-olefins reaction is highly exothermic and may have a large amount of water. The effluent stream derived from an oxygenate-to-olefin process may include as much as one half of the total weight of the effluent stream as water. Consequently, the water must be removed by condensation in a quench device or a quench tower to isolate the olefin product. The stream is considered an effluent stream from the point the effluent stream exits an oxygenate-to-olefin reactor to the point the gaseous output stream is quenched; quenching the effluent stream produces a quenched effluent stream.
As used herein, “quench device”, also known as a “quench tower”, is a device for introducing a sufficient quantity of liquid quench medium to a gaseous effluent stream where the quench medium may condense at least a portion of the material in the effluent stream. A quench tower is a type of quench device having more than one quench stage. A “quench medium” is defined as a liquid that contacts the effluent stream to cool the effluent stream to the condensation temperature of water.
Generally, the step of quenching the effluent stream forms a quenched effluent stream and a liquid fraction or quench bottoms stream. As used herein, the terms, “liquid fraction” and “quench bottoms stream” are used interchangeably and refer to the portion of the effluent stream and quench medium that is liquid under quench conditions and includes all streams that contain the condensed portion of the effluent stream and fractions of the condensed effluent stream. The term “quenched effluent stream” refers to the portion of the effluent stream that is predominantly gaseous after at least one stage of quenching. Water from the quench bottoms stream may be treated or processed to remove the entrained hydrocarbons (e.g. quench oil, pyrolysis, gasoline, etc.) and potential coke fines that may foul heat exchangers and boilers, lead to poor separation in stripping units, increase energy consumption, and the like.
After treatment to the water, the water may be fed into a dilution steam system where steam may be added to the quenched effluent stream to reduce the partial pressure of hydrogen and shift the equilibrium toward a higher olefin yield. Dilution steam condensate is defined herein as the water condensed from a quench device prior to being treated for use in a dilution steam system, which is different from a dilution steam, i.e. water condensed from the quench device that has been treated for use in a dilution steam system. The refinery stream passes through the dilution steam system and eventually into the distillation tower.
The refinery stream enters the distillation tower as a vapor. As the vapor rises through the distillation tower, the vapor begins to cool. When a substance within the vapor reaches a height within the distillation tower where the temperature of the distillation tower is equal to the substance's boiling point, the substance will condense to form a liquid. The substance with the lowest boiling point will condense at the highest point in the tower, and substances with higher boiling points will condense lower in the tower. Trays within the distillation tower collect the liquid fractions, and the liquid fractions are passed to condensers, which cool the liquid fractions further.
The quench medium, the effluent stream, dilution condensate, dilution steam, and/or the distillation vapor often contain byproducts including oxygenate byproducts, such as carbon dioxide, organic acids, aldehydes, and/or ketones. Furthermore, depending upon operating conditions, unreacted oxygenates may be present in the effluent stream of the oxygenate-to-olefin reaction.
Neutralizing additives may contact the quench medium, the effluent stream, and/or dilution steam to alter the pH thereof. Measuring the pH of the quench medium, effluent stream, and/or dilution steam has been difficult because the electrodes are typically glass and foul quickly. In addition, the reference junction of pH electrodes and the internal filling solution may also become contaminated.
It would be desirable if alternative methods of measuring the pH of refinery streams were devised to alleviate some of these problems.